Preheat the oven to 190C/375F/Gas 5. Peel the apples and cut them in half lengthways, then remove the core and squeeze the lemon onto the flesh. In a 20cm non-stick ovenproof frying pan, cook the butter and sugar gently together with the vanilla until it turns chestnut brown. Add the salt and then the apples and place into the oven for about 10 minutes.

Roll out a disc of pastry that will fit into the pan. Lay the pastry over the apples and prick with a fork, then return to the oven. Bake for 15-20 minutes until the pastry is nicely browned.